Multirange meter



May 14, 1946. R. w; CLARK 2,400,190

MULTIRANGE METER Filed Jan. 12, 1944 5 0 trg /5 vvvvvvv Iv IN VEN TOR.

Patented May 14, 1946 2,400,190 MUL'rmANGE METER Robert W. Clark, Teaneck, N. `Lassignor to Radio Corporation of America, a corporation of Delaware Application .mim 12, 1944, serial No. 517,951 'somma (Cim-9 5) The present invention relates to multi-range meters and, more particularly, to meter systems -which automatically select the proper scale to produce easier reading on the meter.

An object of the present invention is the provision of a meter circuit capable oi indicating any of several scale readings, automatically seiecting the proper scale for maximum ease in, reading.

A further object of the present invention is the provision of a meter circuit which protects the metermovement against any but gross overloads.

The foregoing objects, and others which may appear from the following detailed description, are accomplished by providing a single meter of the desired sensitivity to cover the lower of the two scale ranges and, further, providing a relay which operates at a certain voltage and releases at a lower voltage, these voltages being such that for increasing scale 'readings'at the higher voltage a multiplying resistance is placed in the meter circuit, while ior decreasing scale readings the multiplying resistor is maintained in the circuit until the lower Voltageis reached before the scale reading is changed.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which:

Figure 1 illustrates in diagrammatic form a portion of a circuit including a meter adapted to read two current ranges by appropriate selec- ,l

tion of series resistances; while Figure 2 illustrates an embodiment of th present invention wherein the selection is automatically accomplished.

ln Figure 1 there is shown a current supply lead from a source to a current load. In series with this current supply lead is a resistor it).

The voltage .drop across resistor l is appliedl to a meter M through series resistors il and ,be increased so that it gives a full scale indication for milliainperes. The desired results may be obtained, when using a 1.5 milliamperes meter having a resistance of 40 ohms or thereabouts, if resistor lll has a value of 10 ohms, resistor il, 50 ohms and resistor l2, 900 ohms.` These resistor values will be modified depending on the current through the relay coil.

In Figure 2 a relay 20 is provided having a pair of normally closed contacts 22 and 24. Contacts 22 are shunted across the resistor l2 which changes the sensitivity of vthe meter from 15 to 150 milliamperes. Contacts 24 are connected across a resistor 25 in series with the actuating winding of relay 20. The actuating Winding of @s inserted in the relay operating circuit so as the load current decreases from a value above l5 mllliamperes to a predetermined lower value, say 10 milliamperes, that at this current the voltage drop et across the relay winding is such that the relay will become inoperative, thus closing y contacts 22 andA 2li and returning the meter to the l5 milliampere iull scale sensitivity.

The relay 20 is preferably a fast acting one so that if the load current suddenly increases to the order of milliamperes, the relay operates before the meter M can be damaged.

have shown in Figure 2 one means by which the scaleinuse can be indicated. An extension 30 is provided on the armature 3l of relay 2D which'extends back of'an aperture 32 on the scale or meter M. The words "multiply by are printed to the left of aperture 32 and the armature extension 30 carries the figures 1 and 10 on the end in such positions that when the relay armature 3l is not operated, the numeral 1" appears in aperture 32, and when the relay 'armature 8| isactuated, numeral 10 appears. If desired, the relay armature extension 30 may extend the full length of the meter dial, and each of the major scale graduations on the meter dial may be replaced by apertures similar to aperture 32. IThe extension arm 30 may then carry two sets of numbers adapted to be selectively displayed in the apertures on the meter dial in resistor and the remainder of the meter organA ization, including meter M, relay 20 and the associated resistors in a separate portable case which is provided with a plug for connection across resistor i0 when desired. Thus a single meter organization may be used to measure currents in diierent equipment units.

While I have illustrated a particular embodiment of the present invention, it"shou1d be clearly understood that it is not limited thereto since many modiiications may be made in the several elements employed and in their arrangement, and it is therefore contemplated by the appended claims to cover any such modifications as fall within the spirit and scope of the invention,

Having now described my invention, what I claim as new and desire to have protected by Letters Patent is:

1. A current measuring system including a series resistor connected in a circuit carrying the current to be measured, a meter adapted to measure the potential drop across said resistor, a relay having an armature adapted to operate a pair of normally closed contacts and an actuating winding, said actuating winding being connected across said meter and adapted to operate for applied potentials sulcient to cause full scale deflection of said meter, one of said pair of contacts being shunted across an additional series multiplying resistor for said meter and the other of said pair of contacts being shunted across a resistor connected in series with said actuating winding.

2. A current measuring system including a series resistor connected in a circuit carrying the current to be measured, a meter adapted to measure the potential drop across said resistor, a relay having an armature adapted to operate a pair of normally closed contacts and an actuating winding, said actuating winding being connected across said meter and adapted to operate for applied potentials sufficient to cause full scale deflection oi' said meter, one of said pair of contacts being shunted across a resistor connected in series with said actuating "winding, said relay armature carrying an extension arm in cooperative relationship with the dial of said meter and adapted to change the value of the calibrations on said dial as said armature is operated.

3. A current measuring system including a series resistor connected in a circuit carrying the current to be measured, a meter adapted to measure the potential drop across said resistor, a relay having an armature adapted to operate a pair of normally closed contacts and an actuating winding, said actuating winding being connected across said meter and adapted to operate for applied potentials suflicient to cause full scale deiiection of said meter, one of said pair of contacts being shunted across a resistor connected in series with said actuating winding, said meter having a dial with an aperture therein and said relay arm carrying an extension arm operating back of said aperture to selectively display diiierent multiplying factors for said meter scale as said relay is operated.

ROBERT W. CLARK. 

